Circuit breaker with auxiliary resonance circuit



A ril 2, 1968 H. GREBER 3,375,475

CIRCUIT BREAKER WITH AUXILIARY RESONANCE CIRCUIT Filed Sept. 7, 1965 INVENTOR.

United States Patent ABSTRACT OF THE DISCLOSURE This invention relates to a circuit breaker of high current interrupting capacity, which is achieved through insertion of an auxiliary resonance circuit in series with each main contact of the circuit breaker. The auxiliary resonance circuit consists of a condenser and inductance coil, whose magnitudes are so selected that their admittances cancel each other at commercial frequency on which the breaker is used. The auxiliary circuit can be introduced in series with the main circuit either at once, or in steps, first one element then the other. At resonance, the auxiliary circuit represents an infinite impedance that reduces the interrupted current to zero. The invention is suitable only for AC breakers.

The purpose of this invention is to provide a circuit breaker of high current interrupting capacity for application on any voltage levels including high and extrahigh voltages, and capable to replace the much more expensive oil, air blast, and sulfurhexafl'uoride breakers. This purpose is achieved by means of inserting an auxiliary resonance circuit in series with each main contact of the circuit breaker, at the time of its opening the main circuit. The auxiliary circuit can be introduced in series with the main circuit either at once, or in steps. Firstly the coil is inserted in series into the main circuit. Secondly, the capacitor is connected in parallel to the coil. The magnitude of the capacitance is selected so that it forms with the coil in parallel a resonance circuit. Such circuit presents to the current in the main circuit an infinite impedance, which stops the current in the main circuit. Another, not less important object of this invention is to reduce the voltage surge at opening and closing of the main circuit.

The nature of this invention and its further advantages will become clear from consideration of the following specification taken in conjunction with the accompanying drawing.

In this drawing, "FIGURE 1 is a diagram showing the resonance circuit inserted in two steps into the main circuit, with the capacitor linked in parallel with the coil. FIGURE 2 presents a diagram showing the insertion of the auxiliary resonance circuit into the main circuit in one step. In the diagram in FIGURE 3, the resonance circuit is linked to the main circuit through the intermediary of a current transformer. In FIGURE 4 is shown an isometric view of a coil placed in an enclosure which is filled with iron particles, A diagram of two iron foils wound together to form in cross section two parallel spirals, is presented in FIGURE 5, and the perspective view of the two iron foils is shown in FIGURE 6.

In detailed consideration of FIGURE 1, it can be seen that the main contact 1 of the circuit breaker is connected in series with coil 2, which is shunted through the auxiliary contact 3, when the breaker is closed. When auxiliary contact 4 is closed, capacitor 5 is connected in parallel with coil 2. When the breaker is closed auxiliary contact 4 remains open, and auxiliary contact 3 is closed, as mentioned above. When the breaker is about to open, firstly auxiliary contact 3 is opened, thereby introducing coil 2 in series with the main contact 1. Secondly, auxiliary contact 4 is closed, so that capacitor '5 is linked in parallel with the coil 2. After that the main contact 1 is opened.

In the diagram of FIGURE 2 can be noticed that the main contact 6 of the breaker is connected in series with the resonance circuit consisting of coil 7 linked in parallel with capacitor 8. Both coil 7 and capacitor 8 are shunted through the auxiliary contact '9. When the breaker is closed, also auxiliary contact 9 is closed, so that the resonance circuit is out of function. When the breaker is about to open the main circuit, auxiliary contact 9 opens first, and introduces the resonance circuit, consisting of coil 7 connected in parallel with capacitor 8, into the main circuit and in series with the main contact 6 of the breaker.

A variation of the preceding connection diagram is shown in FIGURE 3. The main circuit is not connected directly with the resonance circuit, but is linked to it through the intermediary of a current transformer. In series with the main contact 10 of the circuit breaker is connected the current transformer 11. The secondary of this current transformer serves as an induction coil connected in parallel to capacitor 12. When the main contact 10 of the circuit breaker is closed, the primary of the current transformer is shunted by means of auxiliary cont-act 13. Before contact 10 is opened, auxiliary contact 13 opens first, and inserts the resonance circuit, formed by the secondary winding of the current transformer in parallel with the capacitor, into the main circuit, through the intermediary of the current transformer.

The nature of the resonance circuit is completely immaterial to the functioning of this invention. However, for convenience two particularly suitable forms of a coil, and of a coil combined with a capacitor are presented. In the isometric view shown in FIGURE 4, it can be seen that coil 14 is placed inside an enclosure 15, filled with iron particles 16. These particles are treated with one of the known chemical processes, such as cairlite, which provide them with very thin, but insulating films. A coil placed in such iron particles has a considerably greater inductance than one in air, or one wound on a laminated iron core.

The possibility of combining the coil and the capacitor is presented in FIGURE 5, diagrammatically, the perspective view of this combination is shown in FIGURE 6. In this figure can be seen that two lamination foils 17 and 18, which are covered with thin insulating coats, are wound so as to form in cross section two parallel spiral lines. Each of the foils (form a part of the inductance coil of the resonance circuit. But at the same time, each foil forms a plate of a capacitor. In the diagram in FIGURE 5, the foils are designated with the numerals 17 and 18 and conductor 19 connects them to form a resonance circuit.

In operation of this breaker, before its main contact opens the main circuit, the auxiliary contact opens first and introduces a resonance circuit into the main circuit. The resonance circuit represents an infinite impedance, which stops the flow of current in the main circuit; then the main contact opens this circuit. Similarly, before closing the main contact, the resonance circuit is inserted first into the main circuit. Since the main contact interrupts the main current after it has been reduced by the resonance circuit to almost zero, there is little point to installing this contact in oil or in other insulating media, such as sulfurhexafluoride. There is also no point to providing the main contact with elaborate means for arc interruption, such as blowout coils, air blasts or oil jets. The resonance circuit itself is comparatively inexpensive. It does not have to be insulated for the line to ground voltage. Its current carrying capacity can be very small, since it is called upon to carry current only for a few cycles. Its cooling problems are non-existent. Consequently, this breaker is capable of replacing the much more complex oil, sulfurhexafluoride, vacuum breakers, which are substantially more expensive. There are no voltage limitations in application of the above described circuit breaker.

What has been described and illustrated is what is regarded to 'be the most characteristic embodiments of this invention. It is to be understood that such are merely examples, and that many modifications, variations, rearrangements and changes by addition, omission, and substitution can be made, without departure from the spirit of this invention and its scope as defined by the following claims.

.. What is claimed as new in the art is:

1. A circuit breaker having an auxiliary resonance circuit consisting of a coil and connected to it in parallel a capacitor, said auxiliary circuit is inserted into the main circuit, by means of opening of shunt contact means, before the main contacts of the breaker are opened, said auxiliary resonance circuit is also inserted into the main circuit, through'the intermediary of opening shunt means, beforethe main contacts are closed, and after the closing of the main contacts, said shunt means are closed, thus putting said auxiliary resonance circuit out of function.

2. A circuit breaker as in claim 1, with said shunt means opening first the bypass around the coil, and then con necting said capacitor in parallel to said coil, before the main contacts of said breaker are opened, and said shunt means also opening the bypass around said coil, and then connecting said capacitor in series With said coil, before the main contacts of the breaker are closed.

3. A circuit breaker as in claim 1, with said resonance circuit consisting of said coil and said capacitor, one for each phase, placed outside the tank of said circuit breaker.

References Cited UNITED STATES PATENTS 1,389,255 8/1921 McDonald 336-69 X 2,094,361 9/1937 Lee 317-11 2,849,659 8/1958 Kesselring 3l711 3,223,923 12/1965 Howell 336-69 X MILTON O. HIRSHFIELD, Primary Examiner. J. D. TRAMMELL, Assistant Examiner. 

